Shutter mechanism

ABSTRACT

A shutter is rotatably mounted in a housing for opening and closing a shutter aperture in the housing. The shutter is coupled to a drive unit for unidirectionally rotating the shutter with the same velocity profile to open and close the shutter aperture during each exposure period. This drive unit includes a drive motor and a control circuit having a source of position and velocity reference data and a feedback control loop configurable for either position or velocity control of the shutter as determined by a control command.

BACKGROUND OF THE INVENTION

This invention relates generally to shutter mechanisms and, moreparticularly, to a rotary shutter mechanism for use in a photometricprinting system.

Various shutter mechanisms are employed in photometric printing systemsof the type used, for example, in the semiconductive industry tophotometrically print an image of a photomask or a reticle on asemiconductor wafer by exposing selected regions of a photosensitivefilm on the semiconductive wafer to exposure light passing through thephotomask or the reticle. In order to photometrically print this imageon the semiconductive wafer with high resolution, it is very importantto uniformly illuminate the photomask or the reticle and, hence, theselected regions of the photosensitive film on the semiconductive waferwith the exposure light. The shutter mechanisms conventionally employedin such photometric printing systems control the exposure period, buttypically do not open all portions of the shutter aperture for the samelength of time. Thus, the photomask or the reticle and, hence, theselected regions of the photosensitive film on the semiconductive waferare therefore typically not uniformly illuminated with the exposurelight. In addition to this important drawback, the shutter mechanismsconventionally employed in such photometric printing systems aretypically larger and slower than desired for many photometric printingapplications.

SUMMARY OF THE INVENTION

The foregoing drawbacks of shutter mechanisms conventionally employed inphotometric printing systems may be overcome by employing a rotaryshutter mechanism which, in accordance with the preferred embodiment ofthis invention, has a cylindrical housing with a conically-shapedshutter cover coaxially disposed and fixedly mounted at one end thereof.A conically-shaped shutter provided with a pair of matchingdiametrically-opposite openings in the side thereof is coaxially androtatably mounted within the housing directly adjacent to the shuttercover. As the shutter rotates, it alternately opens and closes acircular shutter aperture provided in the shutter cover in directalignment with the rotational path of the openings in the shutter. Adrive unit is coaxially supported by the housing and is coupled to theshutter for unidirectionally rotating the shutter during each exposureperiod with the same velocity profile for opening and closing theshutter aperture so that all portions of the shutter aperture are openfor the same length of time during each exposure period. Due to both thecoaxial construction of the shutter mechanism and the conical shape ofthe shutter and the shutter cover, the size of the shutter mechanism maybe reduced, thereby also reducing the moment of inertia and increasingthe speed of the shuter mechanism.

In addition to the foregoing, the preferred embodiment of the presentinvention uses an improved control circuit for the shutter mechanismthat provides both position control and velocity control. In previousvelocity control circuits, the controlling (or command) reference inputsignal was typically a fixed or minimally adjustable signal whichoffered little flexibility with respect to many control applications.Furthermore, when running in both velocity and position control modes,previous control circuits offered compromised performance inaccommodating both modes of operation. The improved control circuit ofthe present invention circumvents both of the above-mentioned drawbacks.The use of a controllable reference generator allows the user to selecta velocity profile to precisely suit the performance requirements of theshutter mechanism. A feedback control loop, the topology of which may bealtered under external control, delivers precise, consistantperformance, whether operating in a position or a velocity control mode.When this feedback control loop and the controllable reference generatorare combined and operated under the direction of a common controller,such as a computer, a high-performance control circuit is obtained witha minimized components count.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a portion of a photometric printing systemincorporating a rotary shutter mechanism according to the preferredembodiment of this invention.

FIGS. 2A and 2B are bottom plan and sectional side views, respectively,of the shutter cover of the rotary shutter mechanism of FIG. 1.

FIGS. 3A and 3B are bottom plan and sectional side views, respectively,of the shutter of the rotary shutter mechanism of FIG. 1.

FIG. 4 is a waveform diagram illustrating the velocity profile of theshutter of FIGS. 3A and 3B for one complete cycle of shutter operation.

FIG. 5 is a detailed graph of a portion of the velocity profile of FIG.4.

FIG. 6 is a block diagram of the drive unit, including a drive motor andan improved control circuit according to the preferred embodiment ofthis invention, for driving the rotary shutter mechanism of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a portion of a photometric printingsystem for photometrically printing an image of a photomask or a reticle6 on a semiconductive wafer 8 by selectively exposing a photosensitivefilm on the semiconductive wafer to exposure light passing through thephotomask or the reticle as shown and described, for example, in U.S.patent application Ser. No. 026,722 entitled, "Improved Step-and-RepeatProjection Alignment and Exposure System", filed on Apr. 3, 1979, byEdward H. Phillips, assigned to the same assignee as the presentapplication, and incorporated herein by reference. The exposure light isemitted by a mercury arc lamp 10 fixedly mounted along adownwardly-extending portion of an optical path 12 of the photometricprinting system. An elliptically-shaped reflector 14 surrounds mercuryarc lamp 10 and is fixedly coaxially mounted therewith for projecting abeam of the exposure light emitted by the mercury arc lamp along thedownwardly-extending portion of optical path 12 to a band reflectingplane mirror 16. This mirror is fixedly mounted in optical path 12 at anangle of forty-five degrees with respect to the downwardly-extendingportion thereof so as to deflect the beam of exposure light along alaterally-extending portion of the optical path to a plane mirror 18.

Plane mirror 18 is fixedly mounted in optical path 12 at an angle offorty-five degrees with respect to the laterally-extending portionthereof so as to deflect the beam of exposure light along anupwardly-extending portion of the optical path to a rotary shuttermechanism 20 and, when the shutter mechanism is opened, there to a lightintegrator 22 fixedly mounted in the upwardly-extending portion of theoptical path. Light integrator 22 is employed for providing the beam ofexposure light passing therethrough with a uniform intensitydistribution in the plane of the photomask or reticle 6 and is operablefor doing so provided all portions of the input surface of the lightintegrator are exposed to the beam of exposure light for the same lengthof time. The photomask or reticle 6 is supported in optical path 12 at alocation between the light integrator 22 and the semiconductive wafer 8so that, when the rotary shutter mechanism 20 is opened, an image of thephotomask or reticle may be photometrically printed on thesemiconductive wafer by exposure of selected regions of thephotosensitive film on the semiconductive wafer to the exposure lightpassing through the photomask or the reticle. Plane reflecting mirrors24 and 26, lens 27, and other optics, as shown and described, forexample, in U.S. patent application Ser. No. 026,722, may be employedfor projecting the beam of exposure light from light integrator 22 alongoptical path 12 to the photomask or reticle 6 and, thence, to thesemiconductive wafer 8. In addition, the photomask or reticle 6 and thesemiconductive wafer 8 may be supported on relatively movable stages 28and 30, as further shown, for example, in U.S. patent application Ser.No. 026,722, to facilitate alignment of the semiconductive wafer and thephotomask or reticle before exposing the photosensitive film on thesemiconductive wafer to the exposure light.

In accordance with the illustrated preferred embodiment of thisinvention, rotary shutter mechanism 20 has a cylindrical housing 32 witha cylindrical bore 34 having a conically-shaped end portion 36 ofoutwardly-increasing diameter. Referring now to FIGS. 1, 2A and 2B, acorrespondingly conically-shaped shutter cover 38 ofoutwardly-increasing diameter is coaxially disposed in spacedrelationship to the conically-shaped end portion 36 of housing 32 so asto provide a conically-shaped clearance space 40. The conically-shapedshutter cover 38 is fixedly held in place by securing an annular flange42 thereof to a mating annular shoulder 44 of the conically-shaped endportion 36 of housing 32 with screws or the like. A circular shutteraperture 46 of sufficient size to permit passage of the beam of exposurelight therethrough is formed in the side of the conically-shaped shuttercover 38 and in the adjacent portion of the housing 32. Rotary shuttermechanism 20 is fixedly mounted adjacent to the optical path 12 so thatthe shutter aperture 46 is disposed in direct alignment with theupwardly-extending portion of the optical path for receiving the beam ofexposure light reflected therealong by plane mirror 18.

Referring now to FIGS. 1, 3A and 3B, there is coaxially and rotatablymounted within the conically-shaped clearance space 40 a correspondinglyconically-shaped shutter 48 having a pair of matchingdiametrically-opposite side portions 50 each disposed for fully closingthe shutter aperture 46 as the shutter rotates and anorthogonally-oriented pair of matching diametrically-opposite sideopenings 52, each disposed for fully opening the shutter aperture as theshutter rotates. Before the conically-shaped shutter cover 38 isactually secured in place, a cylindrically-shaped drive motor 54 (suchas an Inland T-1342 DC torque motor manufactured and sold by the InlandMotor Division of the Kollmorgen Corporation) having a field magnet 56and a rotor 58 is coaxially secured in place within the bore 34 ofhousing 32. A cylindrically-shaped hub 60 is inserted through an axialcylindrical bore of the rotor 58, affixed to the rotor, and coaxiallysupported within the bore 34 of housing 32 by bearings 62 for rotationwith the rotor. The conically-shaped shutter 48 is fixedly secured tothe hub 60 with screws or the like so as to rotate with the hub andwithin the conically-shaped clearance space 40. At this point theconically-shaped shutter cover 38 may be fixedly secured in place asdescribed above.

A first shaft 64 is inserted within an axial cylindrical bore of hub 60and affixed to the hub for rotation therewith by a set screw 66 that maybe screwed into place through a clearance opening 68 provided for thatpurpose in housing 32. The first shaft 64 is coupled to a second shaft70 of a potentiometer 72 by a bellows coupling 74 for accomodating anyaxial misalignment of the two shafts and for imparting rotation of thefirst shaft (and, hence, of the shutter 48) to the second shaft so thatthe potentiometer provides an output voltage proportional to therotational position of the shutter. Potentiometer 72 is secured to amotor cover 76 which is coaxially secured in place at the non-conicalend of housing 32 to seal off the cylindrical bore 34 of the housing andprevent dust or other foreign matter from impairing the operation of thedrive motor 54.

The potentiometer 72 is part of a control circuit, hereinafterdescribed, electrically coupled to the drive motor 54 for controllingthe shutter 48. This control circuit drives the drive motor 54 tounidirectionally rotate shutter 48 in one sense (for example, clockwise)with the same velocity profile 78 for both opening and closing theshutter aperture 46 during a first exposure period and tounidirectionally rotate the shutter in the opposite sense (for example,counter-clockwise) with the same velocity profile 80 for both openingand closing the shutter aperture during a second exposure period, asindicated in FIG. 4 for one complete cycle of shutter operation. Thus,all portions of the shutter aperture 46 are open for the same length oftime during each exposure period. This results in all portions of theinput surface of the light integrator 22 being exposed to the beam ofexposure light through the shutter aperture 46 of rotary shuttermechanism 20 for the same length of time during each exposure periodand, hence, in substantially uniform illumination of the photomask orreticle 6 and of the selected regions of the photosensitive film on thesemiconductive wafer 8 with exposure light, as required tophotometrically print an image of the photomask or the reticle on thesemiconductive wafer with high resolution.

Since, as shown in FIG. 4, the velocity profile 78 or 80 for rotatingthe shutter 48 to open the shutter aperture 46 is the same as thevelocity profile 78 or 80 for rotating the shutter to close the shutteraperture during each exposure period, except that the velocity profile78 for the first exposure period and the velocity profile 80 for thesecond exposure period are of opposite polarity, a detailed graph ofonly the velocity profile 78 for rotating the shutter to open theshutter aperture is shown in FIG. 5. Each point on this graph representsa velocity datum stored, for example, in a computer 82 of the controlcircuit (see FIG. 6) and supplied by the computer at the designated timeintervals to generate a precise velocity profile with an optimizedcontour for controlling the position of the shutter 48 as well as anoptimized contour for controlling the velocity of the shutter.

Referring now particularly to FIGS. 1, 5 and 6, each velocity datumstored in computer 82 is supplied as an eight-bit byte to adigital-to-analog converter 84 at the designated time interval (forexample, one byte every five hundred microseconds). Thedigital-to-analog converter 84 converts each such byte to an analogvelocity reference voltage and applies that analog velocity referencevoltage along with a corresponding analog velocity reference voltage ofopposite polarity to a single-pole double-throw switch 86. Computer 82also supplies a two-bit control byte to a control register 88 at eachtransition 90 (see FIG. 4) between position and velocity control toconfigure a feedback control loop 91 of the control circuit as requiredfor the following period of position or velocity control and as furtherexplained in detail below.

Assuming the shutter 48 is initially closed, as at the beginning of thefirst exposure period of each complete cycle of shutter operation,control register 88 sets switch 86 to apply the noninverted analogvelocity reference voltage to the positive input of an error amplifier92 and sets a single-pole double-throw switch 93 to apply an analogvelocity feedback voltage signal from a differentiator 112 through aresistive-capacitive lead network 94 to the negative input of the erroramplifier. Concomitantly, control register 88 opens single-polesingle-throw switches 95, 96 and 98 to configure feedback control loop91 of the control circuit for velocity feedback. When so configured acapacitive network 100 and resistive networks 102, 104, and 106 areoperatively included in the feedback control loop 91. This arrangementof networks provides the feedback control loop 91 with an optimumgain-frequency contour for velocity control. The feedback control loop91 includes a feedback amplifier 108 having its negative terminalconnected to the junction of resistive networks 104 and 106 and havingits positive terminal connected to ground. This feedback amplifier 108provides a stage of amplification of the error signal from erroramplifier 92. A power amplifier 110 is coupled to the output of feedbackamplifier 108 to further amplify the error signal and to supply thepower required to drive the drive motor 54 so as to rotate the shutter48 in accordance with the velocity profile of FIG. 5.

As indicated above, the potentiometer 72 is directly coupled to both theshutter 48 and the drive motor 54 so that the output voltage of thepotentiometer is directly proportional to the rotational position of theshutter 48. The output voltage of the potentiometer 72 is differentiatedby the differentiator 112 to yield the required analog velocity feedbackvoltage signal applied to switch 93 so as to close the feedback controlloop 91 as configured for velocity control.

At the end of each period of velocity control, the shutter 48 isstationary and the feedback control loop 91 is switched to a positioncontrol configuration so as to insure that the next period of velocitycontrol is started at the correct point. The computer 82 thereforesupplies the digital-to-analog converter 84 with an eight-bit bytecontaining desired position information and supplies the controlregister 88 with a two-bit byte for switching the feedback control loop91 to the position control configuration at the end of theabove-described velocity control period. This causes the controlregister 88 to close switches 95, 96 and 98, to set the switch 86 forapplying an analog position reference signal from the digital-to-analogconverter 84 to the positive input of the error amplifier 92, and to setthe switch 93 for directly applying the output voltage of thepotentiometer 72 through the resistive-capacitive lead network 94 to thenegative input of the error amplifier. With switches 95 and 96 closed,resistive network 102 and another resistive network 114 are operativelyconnected in parallel in the portion of feedback control loop 91associated with the error amplifier 92. This yields a resistive feedbackcharacteristic for the error amplifier 92. With switch 98 closed, aresistive-capacitive network 116 is operatively connected in parallelwith resistive network 104 in the position of the fleedback control loop91 associated with the feedback amplifier 108 to further increase thestability of the feedback loop as configured for position control.

I claim:
 1. A servo-control circuit for controlling both velocity and position of a utilization device, said circuit comprising:drive means for moving the utilization device; a reference source of velocity and position reference information indicative of the desired velocity and position of the utilization device; a feedback source of velocity and position feedback information indicative of the actual velocity and position of the utilization device; a feedback control loop coupled to the drive means and to the reference and feedback sources, said feedback control loop having a topology configurable for velocity control of the drive means to control the velocity of the utilization device in accordance with velocity reference and feedback information from the reference and feedback sources and differently configurable for position control of the drive means to control the position of the utilization device in accordance with position reference and feedback information from the reference and feedback sources; and control means, coupled to the feedback control loop, for configuring the topology of the feedback control loop for velocity control of the drive means in response to a command signal and for differently configuring the topology of the feedback control loop for position control of the drive means in response to another command signal.
 2. A servo-control circuit as in claim 1 wherein said feedback control loop comprises:amplifying means, coupled to the drive means and to the reference and feedback sources, for supplying the drive means with an error signal related to the difference between the velocity reference and feedback information when the topology of the feedback control loop is configured for velocity control of the drive means and related to the difference between the position reference and feedback information when the topology of the feedback control loop is configured for position control of the drive means; and network means, coupled in circuit with the amplifying means, for determining the gain-frequency contour of the feedback control loop, said network means including switching means for modifying the gain-frequency contour of the feedback control loop in response to one of the aforementioned command signals.
 3. A servo-control circuit as in claim 2 wherein:said amplifying means comprises a first amplifier having first and second inputs coupled to the reference and feedback sources, respectively, and a second amplifier having an input connected in series with an output of the first amplifier and having an output coupled to the drive means; said network means includes first network means for forming a feedback path from one of the first and second inputs to the output of the first amplifier, and second network means for coupling the output of the first amplifier to the aforementioned input of the second amplifier; and said switching means includes first and second switching means included in said first and second network means, respectively, for modifying the gain-frequency contour of the feedback control loop in response to said one of the command signals.
 4. A servo-control circuit as in claim 3 wherein:said first network means comprises a first pair of networks coupled in parallel from said one of the first and second inputs to the output of the first amplifier; said second network means comprises a second pair of networks coupled in parallel from the output of the first amplifier to the aforementioned input of the second amplifier; said first switching means comprises a switch, connected in series with one of the first pair of networks from said one of the first and second inputs to the output of the first amplifier, for being opened or closed in response to said one of the command signals; and said second switching means comprises a switch, connected in series with one of the second pair of networks from the output of the first amplifier to the aforementioned input of the second amplifier, for being opened or closed in response to said one of the command signals.
 5. A servo-control circuit as in claim 4 wherein:said first network means further comprises an additional network connected in series with the other of the first pair of networks from said one of the first and second inputs to the output of the first amplifier; and said first switching means further comprises an additional switch, connected in parallel with the additional network, for being opened or closed in response to said one of the command signals.
 6. A servo-control circuit as in any of the preceding claims 1-5 wherein said reference source comprises:processing means for storing and selectively providing the velocity and position reference information in a first form compatible with the processing means; conversion means, coupled to the processing means and to the feedback control loop, for converting the velocity and position reference information from the processing means to a second form compatible with the feedback control loop; and means for coupling the conversion means to the feedback control loop to supply the converted velocity and position reference information from the conversion means to the feedback control loop.
 7. A servo-control circuit as in claim 6 wherein:said processing means comprises a computer for storing and providing the velocity and position reference information in a digital form; and said conversion means comprises a digital-to-analog converter for converting the digital velocity and position reference information from the computer to analog velocity and position reference information for the feedback control loop.
 8. A servo-control circuit as in claim 6 wherein said feedback source comprises:first feedback source means for monitoring the position of the utilization device; second feedback source means for monitoring the velocity of the utilization device; and means for coupling the first and second feedback source means to the feedback control loop to supply the velocity and position feedback information from the first and second feedback source means to the feedback control loop.
 9. A servo-control circuit as in claim 8 wherein:said first feedback source means comprises a potentiometer for producing a signal indicative of the actual position of the utilization device; and said second feedback source means comprises the potentiometer and a differentiator for producing a signal indicative of the actual velocity of the utilization device.
 10. A servo-control circuit as in claim 8 wherein said control means comprises:processing means for selectively providing the command signals; and register means, coupled to the processing means and to the feedback control loop, for receiving the command signals from the processing means to configure the topology of the feedback control loop for velocity control of the drive means in response to the first-mentioned command signal and to differently configure the topology of the feedback control loop for position control of the drive means in response to the second-mentioned command signal.
 11. A servo-control circuit as in claim 10 wherein the register means is also coupled to the reference and feedback sources for selectively controlling the application of reference and feedback information from those sources to the feedback control loop.
 12. A servo-control circuit as in claim 10 wherein:said drive means comprises a motor; and said utilization device comprises a shutter. 